Emilia Clarke and Jai Courtney shoot out of a moving van at a liquidy terminator, |Paramount Pictures

In the fifth “Terminator,” Arnold Schwarzenegger says “I’ll be back” once but “I’m old, not obsolete” at least three times, maybe four. Like “Jurassic World,” this latest exhuming of a very, very old franchise — starring a star whose post-pol comeback has been rough, to say the least — is acutely aware of itself and, more to the point, aware of its own potential irrelevancy. It has some shoehorned-in explanations for, for instance, why it stars a senior citizen android assassin, but it’s far more worried of not being up with the times. For better but mostly for worse, it fits right into the modern blockbuster: Like a Marvel film, it’s a hodgepodge of stuff, mixing in brainless plotting (involving heady scientific concepts), passing thrills and nostalgia for a happier time of less sloppy blockbusters, including 1984, the year of “The Terminator,” and 1991, the year of “Terminator 2: Judgment Day.”

Indeed, “Terminator: Genisys” — there’s also a pretty good explanation of its bothersome title — begins by flat-out recreating the first one. Once again post-apocalyptic savior John Connor (now Jason Clarke) has sent bud Kyle Reese (now Jai Courtney) back to 1984 to save/knock up his mom (now Emilia Clarke). There waits the T-800 (a digitally youthenized Ah-nuld) but, alas, also the other, nicer T-800 (today’s Ah-nuld) — apparently just like the one that saved Sarah and John in good old 1991, except this one was sent to 1973 to raise and train Sarah himself. The plan is to head off to thwart “Judgment Day,” which once upon a time happened in 1997 but has since been whimsically postponed till 2017.

Hopefully this isn’t already confusing, though don’t think the “Terminator” entry with more time travel mayhem than the entire series combined should be confused with “Primer.” Despite having an admittedly worthwhile hook, that playfully reworks a classic, it’s clear the script — one of whose writers, Patrick Lussier, penned three of last decade’s forgotten “Dracula” series — doesn’t worry too much about double checking all the time lines to make sure they pan out. Our not-so-secret surprise villain even boasts that he’s not worried about killing someone who’d ensure his basic existence because, five movies in, the number of multiple time lines has gotten too mudded anyway, and so yolo.

The shruggy emoticon ¯\_(ツ)_/¯is the prevailing attitude when it comes to everything in “Genisys,” which keeps throwing twists and ideas and gun fights and chases at ya. Gadgets that can solve unusual problems are always being abruptly introduced, and characters, good and bad, are always able to abruptly return, unless they’re suddenly not. Skynet, the noble corporation that will turn genocidal, has been repurposed as a critique of our real-life gadget happy tech dystopia — but that idea is as momentary as one of its (usually pointless) shoot-outs, forgotten as soon as it’s introduced. The act of sticking it to iPhones and OS gets a shorter lifespan than the film’s revival of the liquidy T-1000 (Lee Byung-hun), who doesn’t even survive a whole reel.

Still, better jam-packed and thoughtless than the relentlessly dour “Terminator: Salvation,” which found no joy in robotic titans stomping about and which has, in effect, and perhaps deservedly, been erased from the series’ timeline. Things are jokier and, more to the point, busier than they were last time, and the number of hairpin plot turns self-consciously recalls the snaky “T2.” But it lacks that film’s precision, and not only because director Alan Taylor — who made “Thor 2” but also made a nice movie about Napoleon in love — is not a James Cameron but a work-for-hire type who can’t even get much out of a helicopter chase.

Emilia Clarke does, for the record, make a fine, fiery Sarah, whose funniest hook is that she’s nervous about informing Kyle that they’ll be doing the nasty once they have some downtime. But the other Clarke, Jason, does little but smirk, and Courtney lacks the relative flamboyance of Michael Biehn. Schwarzenegger is game (and, eventually, gray), and is still unable to wrap his mouth around words like “cellular.” But the film’s message — that the old can still cohabitate with the new — mostly makes the case that one should create something new, not just rehash the past. Or, better yet, one should be inspired by the superior old without throwing up one’s hands and simply copying it.